JP2666218B2 - Engine air-fuel ratio control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an engine, and more particularly to a device for controlling an air-fuel ratio to a target value by feedback control.

(Prior art) To improve fuel efficiency and exhaust performance, for example,
As described in Japanese Patent No. 44752, there is known an air-fuel ratio control device that feedback-controls an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of an engine to an optimum value. This air-fuel ratio control device has an oxygen concentration sensor (hereinafter referred to as an O ₂ sensor) installed in an exhaust passage, and when the residual oxygen concentration in the exhaust gas detected by the sensor is large, the fuel supply amount is compared with the basic supply amount. The air-fuel ratio is adjusted to a predetermined target air-fuel ratio (for example, air / fuel = 14.7) by correcting the increase in the fuel supply amount when the residual oxygen concentration is low, or by correcting the decrease in the fuel supply amount when the residual oxygen concentration is low.
In this case, feedback control is performed so as to converge.

(Problems to be Solved by the Invention) By the way, in air-fuel ratio control using this type of device, deterioration of fuel consumption performance and exhaust performance is avoided during normal operation such as running a vehicle, and good output performance is obtained. Therefore, it is required to control the air-fuel ratio with good responsiveness,
At the time of idling operation in which rotation fluctuation or the like is likely to occur, stable control is required rather than responsiveness, and there is a problem that it is difficult to satisfy both requirements. In other words, if the responsiveness during normal operation is emphasized and the gain of the feedback correction amount for the deviation between the target air-fuel ratio and the actual air-fuel ratio is set to a large value, the change in the fuel supply amount during idling will increase and stability will increase. If the gain is set to a relatively small value, the desired response cannot be obtained during normal operation.

On the other hand, the O ₂ sensor deteriorates with the operation time, and this deterioration causes a change in the actual air-fuel ratio and a change in the output of the O ₂ sensor to increase the fluctuation width of the feedback correction amount. There is also a problem that stability during idling is deteriorated.

The former problem can be dealt with by changing the gain of the feedback correction amount between normal operation and idle operation, but the latter problem can be solved at the same time by this measure. Cannot be done.

On the other hand, an upper limit value and a lower limit value are respectively set on the + side and the − side with respect to the fluctuation of the feedback correction amount, and the width between the both limit values is kept relatively wide at the time of normal operation. While the responsiveness of the control is ensured by not restricting the above-mentioned feedback correction amount, and when shifting to the idle state, the upper and lower limits are changed so that the width between them is reduced, and the feedback correction is performed. A method has been considered in which a change in fuel supply amount is suppressed and the operating state is stabilized by gradually narrowing the allowable fluctuation range of the amount. However, even when this method is adopted, the following problem may occur.

That is, when the basic control amount (basic fuel supply amount) corresponds to the target air-fuel ratio, the feedback correction amount is a positive side (increase side) for converging to the target air-fuel ratio.
The fluctuation amount to the negative side (reduction side) becomes substantially equal to the fluctuation amount to the negative side (reduction side), and the average value becomes substantially 0. The basic control amount is determined by conditions such as the intake air temperature and the fuel temperature. May not correspond to the target air-fuel ratio due to a change in the state of the passage in the fuel supply system or the like. In this case, the average value of the feedback correction amount is biased to the plus side or the minus side. In such a case, as described above, when the state shifts to the idle state and the allowable variation range of the feedback correction amount is reduced uniformly from the + side and the − side, the average value of the feedback correction amount is forcibly set to 0. , And as a result,
The air-fuel ratio cannot be maintained at the target air-fuel ratio.

Further, as described above, when the average value of the feedback correction amount is biased to the positive side or the negative side, this is corrected by the learning control so that the average value of the feedback correction amount substantially matches the zero point. Although it is conceivable to perform the control for reducing the above-mentioned allowable fluctuation range, the learning control requires a relatively long time, so that there is a problem that the fluctuation of the feedback correction amount cannot be suppressed during that time.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problem when the air-fuel ratio is feedback-controlled, and to achieve both responsiveness during normal operation and stability during idle operation.

(Means for Solving the Problems) In order to solve the above problems, the present invention uses the following means.

That is, as shown in FIG. 1, feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to a target value by correcting the fuel supply rate based on the residual oxygen concentration in the exhaust gas. A limit value setting means B for setting an upper limit value and a lower limit value for a change in the amount of feedback correction by the feedback control means A; an idle detection means C for detecting an idle state of the engine; The limit value setting means B when the idle state is detected by the means C;
And limit value control means D for variably controlling the lower limit value. The limit value control means D changes the upper and lower limits at the time of transition to the idle state so that the allowable range of the feedback correction amount is gradually reduced. When the fluctuation range is reached, the change of the limit value is stopped. Then, when the other limit value also reaches the fluctuation range of the feedback correction amount, the two limit values are changed again, and finally the operation is performed so as to reduce the fluctuation allowable width of the feedback correction amount to a predetermined width.

(Operation) According to the above configuration, during normal operation, if the upper limit value and the lower limit value of the feedback correction amount are set to relatively large values by the limit value setting means B, the feedback correction amount becomes smaller than the target air-fuel ratio. In order to eliminate the actual deviation of the air-fuel ratio, a relatively large value can be taken without being restricted by the upper limit and the lower limit. Therefore, the deviation is quickly eliminated and air-fuel ratio control with good responsiveness is performed.

On the other hand, when the state shifts from this state to the idle state, the limit value control means D changes the upper limit value and the lower limit value of the feedback correction amount so that the width between them is gradually reduced. The value is gradually limited, whereby a rapid change in the fuel supply amount is suppressed, and stable idling is realized. In this case, particularly in the present invention, the limit value control means D temporarily stops the change of the limit value when either the upper limit value or the lower limit value reaches the fluctuation range of the feedback correction amount. Then, only the other limit value is changed, and when the other limit value reaches the fluctuation range of the feedback correction amount, the two limit values are again changed. Therefore, even when the average value of the feedback correction amount is deviated to the plus side or the minus side from the zero point, the fluctuation allowable width is reduced to a predetermined width centering on the average value. At times, stable control is performed while accurately maintaining the air-fuel ratio at the target air-fuel ratio.

(Examples) Hereinafter, examples of the present invention will be described.

First, the configuration of an engine control system to which the present embodiment is applied will be described with reference to FIG.
It has an intake passage 5 and an exhaust passage 6 which communicate with the combustion chamber 4 via intake and exhaust valves 2 and 3, and an air cleaner 7, an air flow meter 8 and a throttle valve 9 are arranged in the upstream of the intake passage 5 and downstream. A fuel injection valve 10 is disposed in the intake passage 5, and a bypass passage 11 that bypasses the throttle valve 9 is provided in the intake passage 5.
A bypass control valve 12 for controlling the amount of bypass air is provided above. Further, a catalyst device 13 for purifying exhaust gas is provided in the exhaust passage 6, and an O ₂ sensor 14 for detecting the concentration of residual oxygen in the exhaust gas is disposed upstream of the catalyst device 13.

On the other hand, this engine control system is provided with a control unit 20 for controlling various states of the engine 1,
The control unit 20 detects an intake air amount signal a from the air flow meter 8, a throttle opening signal b from a throttle sensor 21 for detecting the opening of the throttle valve 9, and also detects a fully closed state of the throttle valve 9. and the idle signal c from the idle switch 22, an engine speed signal d from the distributor 23, the oxygen concentration signal e and the intake air temperature sensor 24 and water temperature sensor for detecting intake air temperature and the engine coolant temperature respectively from the O ₂ sensor 14 twenty five
, A water temperature signal g, a neutral signal h from a neutral switch 26 for detecting a neutral state of a transmission (not shown), and a starter signal i from a starter switch 27 for detecting operation of an engine starter. Etc. are input.

Then, the control unit 20 receives the input signals a
To i, outputs a fuel control signal j for controlling the fuel injection amount to the fuel injection valve 10,
At the time of idling, a signal k for controlling the amount of bypass air is output to the bypass control valve 12 to control the idle speed, and an ignition timing control signal for controlling the ignition timing of an unillustrated spark plug is output. It is supposed to.

Here, an outline of the fuel control will be described. The control unit 20 calculates an intake air amount per intake cycle based on the intake air amount signal a and the engine speed signal d, and corresponds to the air amount. The basic fuel injection amount is set, and the value is corrected as necessary to determine the final injection amount. Then, a fuel injection signal j is output to the fuel injection valve 10 so as to achieve this injection amount. At this time, the air-fuel ratio converges to the target air-fuel ratio based on the residual oxygen concentration signal e from the O ₂ sensor 14. Feedback control is performed so that the This feedback control, if the residual oxygen concentration in the exhaust gas detected by the O ₂ sensor 14 is a predetermined value or more, the air-fuel ratio is determined to be leaner than the target air-fuel ratio, for increasing the fuel injection amount The feedback control amount is corrected as described above, and when the residual oxygen concentration is equal to or less than a predetermined value, it is determined that the air-fuel ratio is richer than the target air-fuel ratio,
The control amount is corrected so as to reduce the fuel injection amount.

In particular, in the present invention, the feedback control of the air-fuel ratio is performed by increasing or decreasing the fuel injection amount so as to control the air-fuel ratio to the target air-fuel ratio with good responsiveness during normal operation and to make the rotation speed as stable as possible during idling. The lower limit is variably controlled above and below the feedback correction amount to be made.

Next, the specific operation of the above-described limit value control of the feedback correction amount will be described with reference to the flowcharts of FIGS.

In this control, when the engine 1 is started, the control unit 20 first performs an initial value setting operation according to a flowchart shown in FIG. That is, each of +25% the upper limit L ₁ and the lower limit value L ₂ for the feedback correction amount C _FB, - set to 25%, also +25 percent memory values M _1, M ₂ of these limits, respectively, - 25 % (Steps S ₁ ′, S ₂ ′). A reduction permission flag F ₁ , which is set to “1” when the upper limit L ₁ and the lower limit L ₂ are changed so as to reduce the width therebetween, and set to “0” when the change is prohibited. set F ₂ to each "1" (step S ₃ '). Here, as shown in FIG.
L ₁ and +25% of the lower limit value L _2, - the value of 25%,
This value is sufficiently larger than the fluctuation range of the feedback correction amount C _FB during normal operation.Therefore, the fluctuation of the feedback correction amount C _FB is not regulated by these limit values L ₁ and L ₂ during normal operation. The air-fuel ratio is controlled to the target air-fuel ratio with good responsiveness by the feedback correction amount C _FB having the magnitude of.

Next, the control unit 20 determines the value of the fourth run to the flowchart in Figure, first idle flag Fi at step S _1. This flag Fi corresponds to the signals c and h from the idle switch 22 and the neutral switch 26 shown in FIG.
Is set to “1” when it is determined that the engine 1 is in an idle state based on the above, otherwise it is set to “0”. Now, assuming that Fi = “1” ,
Next, in Suttepu S _2, determines the value Fi 'at the time of the previous determination of the flag. Then, Fi '= when it is "0", that is, when the present control cycle is immediately after the transition to the idle state, each of the upper limit value L ₁ and the lower limit value L ₂ for the feedback correction amount C _FB in step S ₃ (+25% in the operation beginning, - 25%) memory values M _1, M ₂ substitutes, then, the upper limit L ₁ of the feedback correction amount C _FB in step S ₄
Determining the value of the reduction permission flag F ₁ for, for this upper limit L ₁ when F ₁ = _"1", on the operation of width between the lower limit value L _1, L ₂ is varied so as to reduce Start.

This operation is performed according to step S ₅ to S _9, step
To the upper limit L ₁ in S ₆ is determined to have become smaller than the feedback correction amount C _FB, is effected by the upper limit value L ₁ is decreased a predetermined amount α tsuzuic in step S _5. And L ₁ <
When it becomes a C _FB, the reduction permission flag F ₁ for the upper limit value is set to "0" in the step S _7, then, the value of the reduction permission flag F ₂ of the lower limit value L ₂ at the step S ₈ Judge,
The flag F ₂ is set to both the flag F _1, F ₂ both "1" when "0".

Similarly, the lower limit value L _1, when the reduction permission flag F ₂ is determined to be "1" in the step S _10, step S
To the lower limit value L ₂ is at ₁₂ is determined to have become larger than the feedback correction amount C _FB, the lower limit value L ₂ in step S ₁₁ alpha
Increase by one. Then, when it becomes the L _2> C _FB, as well as set to "0" to the reduction permission flag F ₂ in step S _13, the value of the reduction permission flag F ₁ for the upper limit L ₁ in step S ₁₄ Judge, and when this is “0”, step S
_{At 15} , both flags F ₁ and F ₂ are set to “1”.

Here, on the above, the lower limit value L _1, specifically described with reference to FIG. 5 a reduced operation of the width between L _2, first on the time T ₀ the transition to the idle state, the lower limit value L _1, because it is L reduction permission flag F ₁ of _2, F ₂ both "1", the upper limit L ₁ is decreased by one alpha, upper and lower limit values L ₂ is being increased by one alpha, between the lower limit value L _1, L ₂ of The width, that is, the variation allowable width X of the feedback correction amount _CFB is uniformly reduced from the + side and the − side.

And now, as shown in the figure, the feedback correction amount C _FB
Is closer to + than point 0,
Will be the upper limit value L ₁ is reduced to the range of variation of the feedback correction amount C _FB at T _1, this time, since L ₁ becomes <C _FB, reduction permission for the upper limit value at step S ₇ of the flowchart flag F ₁ is set to "0". Therefore, in the subsequent next control cycle will be operating to reduce the upper limit L ₁ in step S ₅ is not performed, the upper limit L ₁ is, L ₁ <C _FB
It would be fixed to the value at the time T ₁ became, during this time, only the lower limit value L ₂ is changed (increased). Thereafter, the lower limit value L ₂ at the time T ₂ is reached the variation range of the feedback correction amount C _FB, if in step S ₁₂ of the flow chart is determined that L _2> C _FB, for the lower limit value in step S ₁₃ the reduction permission flag F ₂ is becomes a "0" to be set, since the reduction permission flag F ₁ for the upper limit value in this case has already been set to "0", the step S ₁₅ from step S ₁₄ And both flags F ₁ and F ₂ are set to “1”. Thereby, as shown in FIG. 5, L ₂ >
The upper and lower limits L ₁ and L ₂ are reduced evenly again from the time T ₂ at which the C _FB becomes equal to C _FB , but in this case, the upper limit L ₁ which has reached the fluctuation range of the feedback correction amount C _{FB first} since reduction in had been stopped, the variation allowable width X of the feedback correction amount C _FB is the time T ₂ later, the average value of the correction amount C _FB around the + side and - be equally reduced from the side become.

Then, a predetermined value the allowable fluctuation width X is in the step S ₁₆ X ₀
If it is determined that it has been reduced to, step the both flags F _1, F ₂ in S ₁₇ is set to "0", on that point T ₃ after the lower limit value L _1, L ₂ is a predetermined width X It will be fixed to the state reduced to ₀ . As a result, when shifting to the idle state, the fluctuation range of the feedback correction amount C _FB is regulated to a relatively narrow range, and the fluctuation of the rotational speed due to the rapid correction of the fuel supply amount is suppressed. Thus, a stable idle state can be obtained. In this case, even if the average value of the feedback correction amount C _FB is biased to the positive side or the negative side, the fluctuation range is uniformly regulated from both the positive and negative sides while maintaining the average value. Therefore, the average value of the fuel supply amount does not change due to the regulation of the fluctuation range, so that a stable idle state can be obtained while maintaining the air-fuel ratio at the target air-fuel ratio.

Note that, as described above, the feedback correction amount C _FB
After the fluctuation width reduced by a predetermined width X ₀ or, for some reason the basic fuel supply quantity is changed by a predetermined variation width, as shown in FIG. 6
The ratio of the fuel increase time t ₁ and loss time t ₂ in the range of X ₀ becomes unequal, the ratio of bulking time t ₁ in one variation period t,
That is, when the duty ratio D exceeds 80%, the control unit 20 executes step S ₁₉ from step S ₁₈ of the flowchart, on, by, respectively to the lower limit value L _1, L ₂ adds a predetermined value β The duty ratio D is 80%
Is converged within, also, when the duty ratio D is less than 20%, by executing the step S ₂₁ from step S _20, on,
By subtracting a predetermined value β from each of the lower limit values L ₁ and L ₂ , the duty ratio D converges to 20% or more.

Further, in this way, the duty ratio D is changed from 20% to 80%.
If it is within the range, the control unit 20
Executes the steps S ₂₃ from step S _22, on the time, the average value _{L 0 [= (L 1 +} L 2) / 2] of the lower limit L _1, L ₂ subtracted from the feedback correction amount C _FB Then, correction is performed so that the average value of the feedback correction amount C _{FB becomes} zero. At this time, as shown in FIG. 7, so as to compensate for the subtraction amount of the mean value L _0, the average value as the learning control quantity to the basic fuel injection amount
L ₀ is added, and the value of the feedback correction amount C _FB is corrected to a new value 0 (0 ′).

Furthermore, in this embodiment, when the vehicle shifts to the acceleration state during the reduction operation of the width between the upper and lower limit values L ₁ and L _{2 at the} time of idling as described above, the reduction operation is performed at the next transition to the idle state. Is performed as a continuation of the operation at the time of the previous idle. That is, the idling flag Fi at step S ₁ in the flowchart if it is determined that "0" indicating that it is not idle, the control unit 20, at the time of previous control and then executes step S ₂₄ idling flag Fi 'of determining the value, if it is "1", in other words, this, when the process proceeds from the idle state to the accelerating state, by performing the steps S _25, S _26, as shown in FIG. 8, on at that time T _4, as well as set the value of the lower limit value L _1, L ₂ to the memory values M _1, M _2, respectively, on the lower limit value L
_1, L ₂ and +25%, - are set respectively to 25%. Thus, at the time of transition during or subsequent normal operation from the idle state at the time T ₄ to the accelerating state, that regulation of the feedback correction amount C _FB is released the feedback control of the good air-fuel ratio responsive performed Become. Then, in order to reduce the width between the upper and lower limits L ₁ and L ₂ at the time of the next idle,
If these reduction permission flags F ₁ and F ₂ are both “0”,
That is unless the reduction to a predetermined width X ₀ has been completed, the both flag F ₁ executes step S ₂₈ from step S _27, F
Set ₂ to “1”. Thus, when going to the next idle state, the memory value in step S ₃
Since M ₁ and M ₂ are the initial values of the upper and lower limits L ₁ and L ₂ , as shown in FIG. 8, at the transition time T ₅ to the next idle state, at the time of the previous idle end time T ₄ And the value, the lower limit value L _1, L
Reduction of _2, will be increased operation is started, the time to shrink these width between predetermined width X ₀ can be shortened.

(Effect of the Invention) As described above, according to the present invention, in the air-fuel ratio control device for the engine that performs the feedback control of the air-fuel ratio, the allowable fluctuation range between the upper and lower limit values with respect to the fluctuation of the feedback correction amount at the time of transition to the idle state. If you gradually reduce
This tolerance is reduced without changing the average value of the feedback correction amount. As a result, the air-fuel ratio is controlled with good responsiveness to the target air-fuel ratio during normal operation in which the allowable variation range is set wide, and the feedback correction amount or fuel is controlled while maintaining the air-fuel ratio at the target air-fuel ratio in the idle state. A sudden change in the supply amount is suppressed, and a stable idle state is obtained.In particular, according to the present invention, even when the O ₂ sensor used for this feedback control is degraded, a stable idle state is obtained. Sex will be maintained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention, and FIGS.
FIG. 2 shows an embodiment of the present invention. FIG. 2 is a control system diagram of the engine. FIGS. 3 and 4 are flowchart diagrams showing the operation of upper and lower limit value control with respect to a feedback correction amount in air-fuel ratio control. FIG. 8 to FIG. 8 are time charts of the feedback correction amount showing each operation by this control. 1 ... engine, 20 ... feedback control means, limit value setting means, limit value control means (control unit), 22, 26 ... idle detection means (idle switch, neutral switch).

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Nakao 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (56) References JP-A-63-97850 (JP, A) JP-A-60 −3443 (JP, A) JP 5-63621 (JP, B2) JP 6-92759 (JP, B2)

Claims (1)

(57) [Claims] An air-fuel ratio control device for an engine that feedback-controls an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber to a target value by correcting a fuel supply rate based on a residual oxygen concentration in exhaust gas. Limit value setting means for setting an upper limit value and a lower limit value for a change in the feedback correction amount; idle detection means for detecting an idle state of the engine; and setting the limit value when the detection means detects an idle state. The upper and lower limits set by the means are changed so that the allowable range of variation of the feedback correction amount is gradually reduced, and when one of the limit values reaches the variation range of the feedback correction amount, The change of the limit values is stopped, and when the other limit value also reaches the fluctuation range of the feedback correction amount, both limit values are changed again, and Readback correction amount of the air-fuel ratio control apparatus for an engine, characterized in that the limiting value control means for reducing the variation allowable width to the predetermined width is provided.